reject invalid dates with bad_cronexpr

README.md

@@ -44,6 +44,8 @@ The special characters have the following meaning:
 
 **Note:** the `L`, `W` and `#` special characters are described here for completeness but are **not implemented** by croncpp. An expression that uses one of them is rejected by `make_cron()` with a `bad_cronexpr` exception.
 
+**Note:** an expression describing a date that never occurs, such as `0 0 5 31 2 ?` for the 31st of February, is also rejected by `make_cron()` with a `bad_cronexpr` exception, because it has no next occurrence to compute. February is measured as a leap year, so the 29th is accepted and the 30th is not.
+
 Examples: 
 
 | CRON | Description |

include/croncpp.h

@@ -386,15 +386,43 @@ namespace cron
          }
       }
 
+      inline bool is_field_separator(char const ch)
+      {
+         return ch == ',' || ch == '-' || ch == '/';
+      }
+
       static std::string replace_ordinals(
          std::string text,
          std::vector<std::string> const & replacement)
       {
          for (size_t i = 0; i < replacement.size(); ++i)
          {
-            auto pos = text.find(replacement[i]);
-            if (std::string::npos != pos)
-               text.replace(pos, 3 ,std::to_string(i));
+            std::string const & name = replacement[i];
+            if (name.empty()) continue;
+
+            std::string const value = std::to_string(i);
+
+            size_t pos = text.find(name);
+            while (std::string::npos != pos)
+            {
+               // Only a name standing on its own is a name. Replacing it
+               // wherever it appears turns "JAN1" into "11", which is a
+               // perfectly good month number and quietly means November.
+               size_t const end = pos + name.size();
+
+               bool const at_start = pos == 0 || is_field_separator(text[pos - 1]);
+               bool const at_end = end == text.size() || is_field_separator(text[end]);
+
+               if (at_start && at_end)
+               {
+                  text.replace(pos, name.size(), value);
+                  pos = text.find(name, pos + value.size());
+               }
+               else
+               {
+                  pos = text.find(name, pos + 1);
+               }
+            }
          }
 
          return text;
@@ -581,6 +609,35 @@ namespace cron
          return INVALID_INDEX;
       }
 
+      // Reports whether any day the expression asks for can occur in any month
+      // it asks for. February is measured as a leap year, so the 29th counts
+      // as reachable and the 30th does not.
+      //
+      // Both bitsets are indexed from the traits minimum, and every traits
+      // type numbers January and the first of the month as that minimum, so
+      // bit 0 is January and day 1 whatever the traits are.
+      inline bool has_reachable_date(
+         std::bitset<31> const & days_of_month,
+         std::bitset<12> const & months)
+      {
+         static int const last_day_of[12] =
+            { 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };
+
+         for (size_t month = 0; month < months.size(); ++month)
+         {
+            if (!months.test(month)) continue;
+
+            for (size_t day = 0; day < days_of_month.size(); ++day)
+            {
+               if (days_of_month.test(day) &&
+                   static_cast<int>(day) + 1 <= last_day_of[month])
+                  return true;
+            }
+         }
+
+         return false;
+      }
+
       inline int field_value(
          std::tm const & date,
          cron_field const field)
@@ -986,6 +1043,12 @@ namespace cron
 
       detail::set_cron_month<Traits>(fields[4], cex.months);
 
+      // A date such as the 31st of February never arrives, so there is no
+      // next occurrence to compute and the expression is rejected here rather
+      // than leaving the caller to make sense of a search that never succeeds.
+      if (!detail::has_reachable_date(cex.days_of_month, cex.months))
+         throw bad_cronexpr("Date specified by the expression is invalid");
+
       cex.expr = expr;
 
       return cex;

test/test_oracle.cpp

@@ -114,6 +114,29 @@ TEST_CASE("oracle: invalid days of week", "[oracle]")
    CRON_EXPECT_EXCEPT("* * * * * 0-8");
 }
 
+TEST_CASE("oracle: month and day names have to stand on their own", "[oracle]")
+{
+   CRON_EXPECT_EXCEPT("0 0 0 1 JAN1 *");
+   CRON_EXPECT_EXCEPT("* * * * * MON1");
+
+   // oracle numbers the months from 0, so JAN is 0 and DEC is 11
+   CRON_ORCL_EQUAL("* * * * JAN *", "* * * * 0 *");
+   CRON_ORCL_EQUAL("* * * * JAN,DEC *", "* * * * 0,11 *");
+   CRON_ORCL_EQUAL("* * * * * MON-FRI", "* * * * * 2-6");
+}
+
+TEST_CASE("oracle: dates that never occur", "[oracle]")
+{
+   // oracle numbers the months 0 (January) to 11 (December), so February is 1
+   CRON_EXPECT_EXCEPT("0 0 5 31 1 ?");
+   CRON_EXPECT_EXCEPT("0 0 0 30 1 *");
+   CRON_EXPECT_EXCEPT("0 0 0 31 3 *"); // April
+
+   REQUIRE_NOTHROW(make_cron<cron_oracle_traits>("0 0 0 29 1 *")); // leap day
+   REQUIRE_NOTHROW(make_cron<cron_oracle_traits>("0 0 0 31 0 *")); // January
+   REQUIRE_NOTHROW(make_cron<cron_oracle_traits>("0 0 0 31 2 *")); // March
+}
+
 TEST_CASE("oracle: every day of the week is reachable", "[oracle]")
 {
    // 2023-09-03 is a Sunday; oracle numbers the days 1 (SUN) to 7 (SAT)

test/test_standard.cpp

@@ -376,6 +376,57 @@ TEST_CASE("standard: invalid days of week", "[std]")
    CRON_EXPECT_EXCEPT("* * * * * /2*-");
 }
 
+TEST_CASE("standard: month and day names have to stand on their own", "[std]")
+{
+   // "JAN1" used to be read as "11", which is a valid month number, so the
+   // expression was accepted and quietly meant November
+   CRON_EXPECT_EXCEPT("0 0 0 1 JAN1 *");
+   CRON_EXPECT_EXCEPT("0 0 0 1 1JAN *");
+   CRON_EXPECT_EXCEPT("0 0 0 1 JANJAN *");
+   CRON_EXPECT_EXCEPT("0 0 0 1 JANUARY *");
+   CRON_EXPECT_EXCEPT("0 0 0 1 XJANX *");
+   CRON_EXPECT_EXCEPT("* * * * * MON1");
+   CRON_EXPECT_EXCEPT("* * * * * 1MON");
+   CRON_EXPECT_EXCEPT("* * * * * SUNDAY");
+}
+
+TEST_CASE("standard: names next to a separator are still names", "[std]")
+{
+   CRON_STD_EQUAL("* * * * JAN *", "* * * * 1 *");
+   CRON_STD_EQUAL("* * * * JAN,FEB *", "* * * * 1,2 *");
+   CRON_STD_EQUAL("* * * * JAN-MAR *", "* * * * 1-3 *");
+   CRON_STD_EQUAL("* * * * JAN/2 *", "* * * * 1/2 *");
+   CRON_STD_EQUAL("* * * * FEB-DEC/3 *", "* * * * 2-12/3 *");
+   CRON_STD_EQUAL("* * * * * MON-FRI", "* * * * * 1-5");
+   CRON_STD_EQUAL("* * * * * SUN,SAT", "* * * * * 0,6");
+
+   // a name repeated in a list is replaced every time, not just the first
+   CRON_STD_EQUAL("* * * * JAN,JAN *", "* * * * 1 *");
+   CRON_STD_EQUAL("* * * * * MON,MON,FRI", "* * * * * 1,5");
+}
+
+TEST_CASE("standard: issue 7, dates that never occur", "[std]")
+{
+   CRON_EXPECT_EXCEPT("0 0 5 31 2 ?");  // February 31st
+   CRON_EXPECT_EXCEPT("0 0 0 30 2 *");  // February 30th
+   CRON_EXPECT_EXCEPT("0 0 0 31 4 *");  // April 31st
+   CRON_EXPECT_EXCEPT("0 0 0 31 6 *");  // June 31st
+   CRON_EXPECT_EXCEPT("0 0 0 31 9 *");  // September 31st
+   CRON_EXPECT_EXCEPT("0 0 0 31 11 *"); // November 31st
+   CRON_EXPECT_EXCEPT("0 0 0 30,31 2 *");
+   CRON_EXPECT_EXCEPT("0 0 0 31 2,4,6 *");
+}
+
+TEST_CASE("standard: dates that do occur are still accepted", "[std]")
+{
+   REQUIRE_NOTHROW(make_cron("0 0 0 29 2 *"));   // leap day
+   REQUIRE_NOTHROW(make_cron("0 0 0 31 1 *"));   // January has 31 days
+   REQUIRE_NOTHROW(make_cron("0 0 0 31 2,3 *")); // March does too
+   REQUIRE_NOTHROW(make_cron("0 0 0 30 2,3 *"));
+   REQUIRE_NOTHROW(make_cron("0 0 0 31 * *"));
+   REQUIRE_NOTHROW(make_cron("0 0 0 * 2 *"));
+}
+
 TEST_CASE("standard: unsupported special characters", "[std]")
 {
    CRON_EXPECT_EXCEPT("0 0 12 L * ?");